Recent years have seen the establishment of a number of independent, common-carrier long-distance telephone networks. These networks compete with the "long lines" network that, until recently, was the only link between many of the local telephone operating companies and, indeed, often between cities served by the same local operating company. This latter system is hereinafter referred to as the "integrated system".
In general, to be able to utilize an independent long-distance calling network, a telephone user must subscribe both to the local telephone company servicing his area and to the long-distance network's service. The long-distance network opens for him an account and assigns to him an identification number. To place a long-distance call over the network, the user employs his local telephone system to place a telephone call to a local office of the long-distance network. This local office, which serves as a gateway into the network, includes a switching system which "answers" the call automatically and then returns a "readiness" tone to signal its readiness to accept a destination telephone number. When the user detects this "readiness" tone, he then dials in the number of the telephone he is calling (i.e., the "destination" number) along with his identification number and perhaps some billing instructions, also. The long-distance network then establishes a connection to the central office of the local telephone network serving the remote, destination telephone being called. A local telephone circuit is then established between that remote central office and the destination telephone.
When the user of the long-distance network calls into the network to place a call, the switching system which controls the network determines, prior to routing the call, whether the destination telephone number is accessible through the long-distance network. If not, the customer is so advised, typically by a prerecorded message, and the network terminates the connection. Thus the customer has to pay for the local call into the network gateway even when his call cannot be placed via the network; further, some network resources have been occupied without any revenue-raising activity having occurred. Also, time has been lost in a non-productive activity. It is highly desirable, therefore, from the view points of the user and the network, to attempt to minimize the number of calls into the network for destination telephone numbers not accessible though the network.
Heretofore automatic dialers have been employed at the subscriber's (i.e., user's) premises in an effort to reduce the number of fruitless attempts to place calls via the long-distance network to telephones not accessible through the network. A typical prior art automatic dialer includes a network directory listing telephone area codes and exchanges accessible via the independent long-distance network (or, equivalently, it may include a directory of telephone area codes and exchanges not accessible via the network, or a directory of network calling restrictions from the user's location, or some combination thereof). When such an automatic dialer is used, a long distance call is placed by dialing the destination telephone number, complete with area code, as prescribed by the integrated system, in normal fashion. The automatic dialer intercepts the call and compares the destination telephone number with the entries in its network directory, to ascertain whether the call can be routed via the independent network. If it can, the automatic dialer places the call through the independent long-distance network in accordance with the calling protocol of the latter. Conversely, if the destination telephone number is found to be not accessible via the independent long-distance network, the call is placed instead via the conventional, integrated telephone system.
As the independent network grows, additional areas become accessible through it. Further, the geographical coverage of telephone area codes and exchanges may be altered from time to time, sometimes changing the geographical coverage provided by the network. Specifically, such changes may render accessible exchanges (and even entire area codes) not previously on the network or render inaccessibe exchanges previously available on the network. Thus it is desirable to provide a way to alter the network directories in the dialers from time to time to reflect changes in the area codes and exchanges accessible through the network. This has been done in the past by storing the directory in a removeable memory element in each dialer and replacing the memory element from time to time with another memory element containing an up-to-date version of the directory. With this approach, it is therefore necessary either to tolerate the dialing via the network of inaccessible destinations (at the cost of the user's time and expense and an increase in the network overhead) or to incur the cost of manufacturing and distributing new network directories from time to time. And if the memory element is not replaceable by the user, this includes the cost of sending a technician to the user's location to effect the replacment.
It is therefore an object of this invention to provide an automatic telephone dialer for controlling access to a long-distance telephone network, in which the expense of updating network directories is considerably reduced, without unduly increasing the number of attempts to place calls via the network to telephone exchanges inaccessible through the network.
Another object is to provide an automatic dialer for long-distance telephone network access control, which is adaptable to changes in the coverage provided by the network without requiring physical replacement of hardware.